296 MOLLUSCA. PECTINIBRANCHIA, 



PECTINIBRANCHIA. 



CRYPTOBRANCHIA. 



Heart entire, and detached from the rectum. Sexes distinct on dif- 

 ferent individuals. The shells of the female more ventricose in the 

 body-whorl than those of the male. 



a. Shell external. 



b. Aperture of the shell entire, together with the anterior margin 

 of the cloak at the entrance of the branchial cavity. Holos- 

 tomata. 



c. Foot with a lid for closing the aperture of the shell. Tec- 

 tipeda. 



TuRBONiDiE. Aperture of the shell ovate or round. 



NeritadjE. Aperture semicircular, with an oblique 

 straight pillar-lip. 



Trochusid^e. Aperture subquadrangular. 



cc. Foot destitute of a lid. Nudipeda. 

 Janthina. 

 Velutina. 



bb. Aperture of the shell canaliculated, for the reception of the sy- 

 phon of the branchial cavity. Solenostomata. 



aa. Shell internal. 

 Sigaretus. 



